1. Field of the Invention
The present invention relates to an electron beam generator, and specifically to an electron beam generator for multiple columns, which is used in each of multiple columns where beams of electrons are used respectively.
2. Description of the Prior Art
An electron beam exposure system of a conventional type is configured to generate a single beam of electrons by use of a single acceleration voltage in a single column. Because of this configuration, the electron beam exposure system of the conventional type has a disadvantage that drawing throughput is slow.
For the purpose of solving this disadvantage, study has been made for a multiple-electron-beam exposure system which performs drawing through generating a plurality of beams of electrons from a single beam of electrons accelerated by an acceleration voltage. The multiple-electron-beam exposure system is capable of simultaneously transferring a plurality of drawing patterns on a workpiece by irradiation, and aims at enhancing throughput.
As a technology concerned with this, Japan Patent Laid-open Official Gazette No. 2002-164009 has disclosed an electron beam generator which generates a plurality of beams of electrons from a single beam of electrons for the purpose of increasing a production rate at which semiconductor elements and the like are produced.
What is required of an electron beam exposure system is an increased drawing throughput, and a capability of drawing fine patterns with a higher precision.
As a technology concerned with this, Japan Patent Laid-open Official Gazette No. Hei. 5-251315 has disclosed an electron beam exposure system which adjusts properties of a plurality of beams of electrons individually, and which thus arranges spot shapes respectively of the plurality of beams of electrons with a higher precision.
In addition, Japan Patent Laid-open Official Gazette No. 2005-26241 has disclosed an electron beam generator which is capable of controlling electric current amounts respectively of the beams of electrons with a higher precision by use of a self-bias resistance, and which thus supplies a stable emission electric current.
FIG. 1 shows a diagram of a schematic configuration of the electron beam generator using the self-bias resistance, which has been disclosed in Japan Patent Laid-open Official Gazette No. 2005-26241. The electron beam generator includes a cathode 1, a grid 2, a filament electric current supply 7, a cathode power supply 4, a self-bias resistance 3, a cathode voltage detector 6 and a cathode controller 5. The cathode 1 generates thermoelectrons. The grid 2 converges the thermoelectrons, and thus forms a beam of electrons. The filament electric current supply 7 heats the cathode 1, and thereby causes the cathode 1 to generate the thermoelectrons. The cathode power supply 4 applies a voltage to the cathodel, and thereby causes the cathodes 1 to emit the thermoelectrons. The self-bias resistance 3 changes the electric potential of the grid 2 relative to the electric potential of the cathode 1. The cathode voltage detector 6 detects the voltage between the electric potential of the cathode 1 and the reference electric potential (earth electric potential). The cathode controller 5 controls the voltage which the cathode power supply 4 applies to the cathode 1 on the basis of the detected voltage.
In the case of the electron beam generator with the foregoing configuration, the thermoelectrons emitted from the cathode 1 constituting an electron gun are accelerated by the voltage applied to the cathode power supply 4. Thus, an emission electric current is generated. When the emission electric current suddenly changes due to discharge or the like, electric potential drop occur between the two ends of the self-bias resistance 3. This electric potential drop causes the electric potential of the grid 2 to change. Thereby, the electric current value of the emission electric current is designed to be inhibited from changing.
As described above, control is made to inhibit the change in the emission electric current, and thereby the emission electric current is stabilized. However, the technology disclosed in Japan Patent Laid-open Official Gazette No. 2005-26241 is intended to deal with a single-column electron beam exposure system, and accordingly no examination has been given to a method of inhibiting change of emission electric current in the multiple-column electron beam exposure system to be intended to increase throughput. As a result, it is unclear whether or not the method adopted for the single-column electron beam exposure system can be adopted to the multiple-column electron exposure system.